The present invention relates generally to medical imaging and, more particularly, to a system and method of imaging a thorax using a variable speed patient-positioning table, preferably in computed tomography systems.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan-shaped beam toward an object, such as a patient. The beam, after being attenuated by the patient, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the patient. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing unit for analysis which ultimately results in the formation of an image.
Generally, the x-ray source and the detector array are rotated with a gantry within an imaging plane and around the patient. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator.
In one known CT imaging system used to image a thorax, imaging is conducted by moving a patient table through a gantry at a constant speed. Generally, the constant table speed is determined by matching the speed of the table to the phase of a patient's cardiac cycle with EKG gating. Problems arise, however, using such a system since the table speed is required to move at a very slow speed throughout imaging in order to have sufficient coverage of the heart at a prescribed phase. Using a slow table speed throughout imaging has several disadvantages such as patient discomfort, limited patient accessibility to the CT system, and a higher x-ray radiation dose to the patient for slower acquisition for the same coverage area. One proposed solution to this problem considered increasing the table speed during imaging. This solution, however, is not suitable for thorax imaging because of the occurrence of motion artifacts. Motion artifacts are caused by motion of the imaged thorax or a part of the imaged thorax, such as the heart, during the imaging sequence causing a blurring in the reconstructed image in the regions where motion occurs. It is well known in the art that motion artifacts can be minimized during imaging of the thorax if the imaging sequence is gated to the cardiac cycle of the patient.
It would therefore be desirable to have a CT imaging system capable of speeding up the imaging time to image a thorax region of a patient without generating motion artifacts in the reconstructed image.